The present invention generally relates to write condition setting methods and disk units, and more particularly to a write condition setting method which sets at least one of a write current that is applied to a head when writing data on a magnetic disk and an off-track slice as a write condition, and to a disk unit which employs such a write condition setting method.
Recently, due to improvements made in the operating speed and performance of computer systems, here are more opportunities to process an extremely large amount of data. For this reason, there are demands to improve the operating speed, storage capacity and performance of magnetic disk units which are often used as auxiliary storage units.
In order to improve the storage capacity of the magnetic disk unit, there is a proposed method which increases the Track Per Inch (TPI) or the Bit Per Inch (BPI), so as to improve the Bit Per Square Inch (BPSI). On the other hand, there is a proposed method which uses a magneto-resistive (MR) head made up of a magneto-resistive element as a read head.
As the TPI becomes large, the interval or pitch of the tracks on which the data are written has becomes extremely small, and it has become necessary to minimize magnetic interference among the adjacent tracks.
When determining a write current which is applied to the head when writing data on the magnetic disk in the conventional magnetic disk unit, the write current is generally determined based on an overwrite characteristic and a saturation characteristic of a head output level. Generally, the magnetic disk unit does not erase the previously written data before writing the new data, and overwrites the new data over the previously written data. For this reason, a residual component of the previously written data remains even after the new data is written over the previously written data by the overwrite. The overwrite characteristic indicates the extent to which this residual component of the previously written data remains after the overwrite. On the other hand, the saturation characteristic of the head output level indicates a maximum level at which the output level of the head saturates by taking the write current as the parameter.
After the write current is determined, the write current is fixedly set with respect to the magnetic disk unit.
When the TPI is large, the magnetic interference with respect to the adjacent tracks becomes more notable when writing the data, due to an error in the positioning accuracy when positioning the head to a predetermined track by moving an actuator mounted with the head, a run out (deviation of the positioning) caused by an eccentricity component of a spindle motor which rotates the disk, an inconsistency of the width of the written track (spreading of the track that is written or, write spread) depending on the accuracy of a code width of the head, and the like. For this reason, a read margin at the time when the data are read from the disk is decreasing.
Conventionally, the write current applied to the head is fixed regardless of the magnetic disk unit. However, the error in the positioning accuracy, the run out, the inconsistency of the written track and the like are slightly different among the individual magnetic disk units due to the slight inconsistencies among the parts used. As a result, there was a problem in that the write current which is fixedly set with respect to the magnetic disk unit may not necessarily be an optimum write current for the magnetic disk unit.
In addition, the parameters such as the error in the positioning accuracy, the run out, and the inconsistency of the written track vary depending on the environment in which the magnetic disk unit is used, and the parameters are particularly affected by the temperature. However, even though the parameters vary depending on the environment, and particularly the temperature, no consideration is given as to the parameters which are dependent upon the temperature when setting the write current in the conventional magnetic disk unit, and there was a problem in that an optimum write current cannot be set with respect to the environment in which the magnetic disk unit is used.
On the other hand, when an off-track slice which indicates a limit value of a positional error quantity of the head with respect to a track which is to be scanned by the head is fixedly set with respect to the magnetic disk unit, an excessive or an insufficient check may be made with respect to the TPI margin, depending on the inconsistencies of the above described error in the positioning accuracy, the run out and the write spread. For this reason, there was a problem in that the TPI margin which is actually used becomes inconsistent depending on the head or the track position.